The present invention relates to a method of removing an unwanted flash portion from a blow molded container and in particular to a method in which the flash portion is gripped and held stationary while the container is either inflated or deflated to change the container size whereby the flash portion is at least partially torn from the container.
In the process of blow molding containers or other articles, the articles are formed from an extruded parison that is held between a pair of mating mold halves expanded outwardly to conform to the shape of the mold cavity. After forming the article, the mold halves are separated and the molded article is ejected. It is common for flash or flashing, which refers to a web projecting from the surface of the container, to be formed at the parting line where the mold halves engage the extruded parison. The flashings must be removed in a separate operation, either by hand or by automatic machines.
Various machines and methods have been employed for removing the flashings. One method is to move the molded container along a path in which a knife cuts the flash from the molded container. In another method, a gripping device grasps the flash and pulls it in a direction away from the molded container to tear the flash from the container. These methods both work well in connection with containers that have a fairly high degree of rigidity to enable the container to retain its shape under the force of the cutting knife or the gripping device. However, for containers that are molded of an elastomeric resin, which are not very rigid, it is difficult to both handle each container with automated machinery and to force the container passed a cutting knife in a controlled fashion so as to cut along the thin section joining the flash to the molded container.
Accordingly, it is a principal object of the present invention to provide an improved method for removing an unwanted flash portion from a blow molded container made from an elastomer or other resin exhibiting elastomeric properties.
The method of the present invention utilizes a gripping device to grip the flash portion to hold it stationary. A fluid flow nozzle is inserted into the opening of the container and fluid is either inserted into the container to inflate the container and increase its size, or fluid is withdrawn from the container to deflate the container and reduce its size. The desired effect of changing the container size is to move the container walls while the flash portion is held stationary. This results in at least a partial tearing of the flash portion from the container. If only a portion of the flash is torn away, the tear facilitates subsequent completion of flash removal either by hand or by other automated means. Depending upon the container configuration and the flash location, the flash portion may be entirely removed by this method.
The decision to use container inflation or deflation is primarily dependent upon the particular container being molded. For a container which generally retains its shape, such as an ear syringe, either inflation or deflation can be used to remove the flash portion. However, with a container that is flexible and generally does not retain its shape, such as a hot water bottle, container inflation is the primary method by which the mold flash is removed. Using deflation for a hot water bottle is not practical. The hot water bottle side walls will collapse upon themselves without causing significant movement of the container walls along the parting line where the flash portion is joined to the molded container.
The method of removing an unwanted flash portion from a blow molded plastic container having a predetermined molded size and an opening, and a flash portion joined to the container along the weakened line, comprises the following steps:
1) gripping the flash portion to hold the flash portion stationary; PA1 2) inserting a fluid flow nozzle into the opening in the plastic container; and PA1 3) passing fluid through the nozzle to change the size of the container from the predetermined molded size so that the plastic container is changed in size while the flash portion is held stationary whereby the flash portion is at least partially torn away from the plastic container along the weakened line.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.